introduce g:airline_theme_patch_func (#173).

autoload/airline.vim

@@ -14,6 +14,11 @@ function! airline#switch_theme(name)
   let palette = g:airline#themes#{g:airline_theme}#palette "also lazy loads the theme
   call airline#themes#patch(palette)
 
+  if exists('g:airline_theme_patch_func')
+    let Fn = function(g:airline_theme_patch_func)
+    call Fn(palette)
+  endif
+
   let w:airline_lastmode = ''
   call airline#update_statusline()
   call airline#load_theme()

doc/airline.txt

@@ -60,6 +60,17 @@ values):
   can be overridden by defining a value. >
   let g:airline_theme=
 <
+* if you want to patch the airline theme before it gets applied, you can
+  supply the name of a function where you can modify the palette. >
+  let g:airline_theme_patch_func = 'AirlineThemePatch'
+  function! AirlineThemePatch(palette)
+    if g:airline_theme == 'badwolf'
+      for colors in values(a:palette.inactive)
+        let colors[3] = 245
+      endfor
+    endif
+  endfunction
+<
 * enable/disable usage of patched powerline font symbols >
   let g:airline_powerline_fonts=0
 <